Autoimmune diseases develop when the adaptive immune response targets self-antigens, leading to inflammation and tissue destruction. The innate immune system faces the same fundamental challenge as the adaptive immune system - distinguishing self from non-self antigens - and there is now considerable evidence that recognition of self nucleic acids through toll-like receptors (TLRs) can contribute significantly to sterile inflammation and autoimmunity, with the clearest example being the role played by TLR9 and TLR7 in the pathogenesis of systemic lupus erythematosus (SLE). The major exception has been TLR8, despite its ability to stimulate important inflammatory cytokines such as IL6 and TNF-1, and its expression by multiple cell types involved in inflammatory diseases. The lack of useful animal rodent models, a consequence of the very different ligand specificity of human TLR8 and its rodent orthologs, has proven to be a major limitation in the study of TLR8 biology. Mouse TLR8 lacks the capability of responding to ssRNA ligands, RNA viruses, or small molecules; all of which have been shown to activate human TLR8. We have developed new tools that we hope will help better understand the biology of TLR8. The key objective of this proposal is thus to identify and characterize a lead TLR8 inhibitory oligonucleotide suitable for IND-enabling preclinical and process-development studies. The principal activities will include: Identify an oligonucleotide-based inhibitor of human TLR8 using in vitro assays with human primary cells, Define its specificity against the other TLR pathways, Test its activity in vivo in an acute model, Determine its ability to prevent a TLR8-dependent autoimmune disease in rodents. If successful, the data generated will provide the groundwork for a full-scale development program for a TLR8 inhibitor for autoimmune diseases.